A more nutritious type of rice designed to prevent vitamin A deficiency is a step closer to becoming a commercial crop.

An agreement has been reached between the inventors of the genetically-modified plant and the biotech companies Zeneca and Greenovation to distribute seed for the crop at no extra cost to farmers in developing countries.

According to the World Health Organisation, about 250 million people worldwide are deficient in vitamin A, putting them at risk of permanent blindness and other serious ailments.

The situation is worst in countries where the population is overly dependent on rice as a staple food. Normal rice contains no beta-carotene, the precursor of vitamin A.

'Golden Rice'

The scientists, based at the Swiss Federal Institute of Technology in Zurich, have inserted three genes into a rice variety that make the plant produce large amounts of beta-carotene, also known as provitamin A.

This gives the rice a yellow colour and has led to it being dubbed "Golden Rice".

Under the new agreement, seeds would be distributed to government-run centres and local farmers would be allowed to earn an annual $10,000 without paying royalties.

Greenovation will act as an intermediary between the inventors and Zeneca.

One of the rice's inventors, Professor Ingo Potrykus, said that up to 80 developing nations had been approached across Asia, Africa and Latin America, and that all had welcomed the prospect of receiving the seeds.

Health foods

India and China, although not classified as developing nations by the United Nations, also have been sounded out.

"The response from government agencies has been overwhelming. Interest is enormous," Professor Potrykus said. "There will always be sceptics, especially in Europe, but this is a humanitarian exercise."

Zeneca said it would also develop the rice for the health food markets in developed parts of the world.

However, despite the announcement, the collaborators warned that further research and testing would mean no planting before at least 2003.

GM critic

"Golden Rice seed will not be sold at a higher price than normal seed," Haydn Parry, general manager of Zeneca's plant science division, told the BBC. "For us, this is a fantastic opportunity to marry together our legitimate commercial interests with being able to help the inventors make the technology available to whoever needs it."

But a leading critic of GM technology, Dr Mae Wen Ho, from the Open University in the UK, said Golden Rice was a giant PR exercise to cover up the inherent hazards of gene-altered crops.

"It is much cheaper for poor people to buy vegetables, which are a very good source of vitamin A," she said.